During a pre-delivery phase of a vehicle, that is after the vehicle has been assembled at an assembly plant, and before the vehicle has left the plant, each vehicle subsystem may be tested to ensure that each subsystem is functioning when the vehicle is delivered to a customer. The first key-on event of a vehicle engine, which may occur after vehicle assembly and before the sale of the vehicle, may be associated with an engine green start condition. During the pre-delivery phase, the vehicle may be started and moved a plurality of times. The vehicle system may include one or more oxygen sensors, such as a Universal Exhaust Gas Oxygen (UEGO) sensor, for engine exhaust air-fuel ratio control. At engine key-on, a UEGO sensor heater may be operated to heat the sensor to a threshold temperature, thereby activating the sensor. Prior to activation of the UEGO sensor, the controller may adjust engine fueling via open-loop control (that is, without receiving input from the sensor) and after activation of the UEGO sensor, the controller may switch to a closed-loop control of engine fueling (that is, with input from the sensor).
Various approaches are provided for heat activating a UEGO sensor. In one example, as shown in US 20070271904, Shouda et al. teaches delaying heating of the UEGO sensor until exhaust temperature increases to above a threshold and water condensation can no longer take place on the UEGO sensor elements. Exhaust temperature is increased by retarding ignition timing for a certain period after engine start. By reducing water condensation on the UEGO sensor elements and by delaying UEGO sensor heating, cracking of UEGO sensor elements due to sudden temperature changes may be reduced.
However, the inventors herein have recognized potential disadvantages with the above approach. As one example, during the pre-delivery phase of the vehicle, the vehicle is operated for shorter durations which may not allow adequate engine operation time for a required exhaust temperature increase. In the approach shown by Shouda et al., operating parameters of the engine (such as spark timing) may have to be adjusted in order to increase the exhaust temperature, however, during the pre-delivery phase, a plurality of vehicle systems may be tested, and it may not be desirable to modify engine operating parameters. Also, retarding ignition timing increases fuel consumption. On the other hand, if heating of the UEGO sensor is expedited during short but frequent engine operations in the pre-delivery phase, water condensate formed on the sensor elements may cause cracks in the sensor. During engine cold-start conditions, there may be an even higher possibility of crack formation in the sensor elements during UEGO sensor heating. Sensor degradation may lead to warranty issues and may cause exhaust emissions to be degraded.
In one example, the issues described above may be addressed by an engine method comprising: during a vehicle pre-delivery phase, feed-back controlling an oxygen sensor heater element to a set-point temperature with a first, lower gain, and during a vehicle post-delivery phase, feed-back controlling the oxygen sensor heater element to the set-point temperature with a second, higher gain. In this way, by adjusting a voltage level to supply a lower electric current to heat the UEGO sensor gradually over a longer period, the sensor may be activated with reduced possibility of sensor elements cracking.
As one example, during a pre-delivery phase of a vehicle, when the vehicle is operated for frequent shorter durations, a lower voltage resulting in a first, lower current may be applied to a UEGO heater to heat the UEGO sensor element. The temperature of the UEGO heater sensor element may be feed-back controlled to a set-point temperature (such as an activation temperature of the UEGO sensor) with a first, lower, gain. Due to the lower current and the lower gain, the UEGO sensor may take a longer time to attain the activation temperature, however, this may be acceptable since the vehicle has not yet been delivered to a customer and since emissions control is less stringent at this time. While the UEGO sensor is slowly heated to the activation temperature, an open-loop fueling control may be used and once the UEGO sensor is activated and capable of measuring exhaust oxygen level, closed loop fuel control may be enabled. During post-delivery phase of the vehicle, when the vehicle is operated for longer durations allowing for adequate warm-up of engine components, a higher voltage resulting in a second, higher current may be applied to the UEGO heater to heat the UEGO sensor element.
Also, the temperature of the UEGO sensor heater element may be feed-back controlled to the set-point temperature with a second, higher, gain in order to expedite UEGO sensor heating such that closed loop fuel control may be enabled within a shorter time after engine start. At this time, expedited sensor heating may be required since the vehicle has been delivered to a customer and since emissions control is more stringent at this time. During conditions when the exhaust temperature is lower than a threshold, spark timing may also be retarded from nominal spark timing to expedite engine exhaust heating such that water in the exhaust system may evaporate instead of condensing on the sensor.
In this way, by using a lower electric current to heat the UEGO sensor element during a pre-delivery phase of the vehicle, the UEGO sensor element may be heated slowly over a longer period of time while at an assembly plant with reduced likelihood of UEGO sensor cracking and degradation. The technical effect of attaining a set-point temperature of the sensor using a lower gain while the vehicle is in the assembly plant is that engine operating parameters may not have to be altered in order to reduce the possibility of UEGO sensor element cracking. In addition to improving fuel economy, vehicle sub-systems tests routinely performed during the pre-delivery phase are not disturbed. In comparison, by transitioning to a higher gain on sensor temperature during the post-delivery phase of the vehicle, UEGO sensor heating may be expedited when the vehicle has left the assembly plant, enabling a faster transition to using feedback control of engine fueling. This improves fuel economy and emissions performance when the vehicle is with the customer. Overall, by using different values of UEGO heater current during pre-delivery and post-delivery vehicle phases, UEGO sensor activation may be optimized while reducing the possibility of UEGO sensor degradation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.